The invention relates to a package for fresh red meat products and the like and, particularly, to a vacuum skin package having a peelable barrier layer and a barrier foam tray.
Skin packaging can be classified as a vacuum forming process for thermoformable polymeric films. The product on a supporting member serves as the mold for the thermoformable film which is formed about the product by means of differential air pressure. However, the term "vacuum skin packaging" or VSP as it is referred to hereinafter, refers not only to the fact that the thermoformable film is formed around the product by vacuum or differential air pressure but also to the fact that the product is packaged under vacuum and the space containing the product is evacuated. Thus, there is a need for the film formed around the product and for the support member to be a barrier to oxygen, air, and other gases.
In conventional skin packaging, a backing board which is porous or which is perforated so that a vacuum may be drawn directly through the backing board is employed. In vacuum skin packaging processes generally a vacuum chamber with an open top is used. The product on an impervious backing board is placed on a platform within the vacuum chamber. The top of the chamber is covered by a sheet of film which is clamped tightly against the chamber to form a vacuum tight closure. The chamber is evacuated while the film is heated to its forming and softening temperature. The platform is then raised to drive the product into the softened film and air pressure can be used above the film to force it tightly around the product. A process of this type is disclosed in French Patent No. 1,258,357 which issued to Alain G. Bresson on Mar. 6, 1961.
A variant of the process described in the Bresson patent is disclosed in French Patent No. 1,286,018 which issued on Jan. 22, 1962 to LaRoach Freres Limited. In the LaRoach Freres process, after the chamber has been evacuated and the product driven into the heat softened film, the vacuum is released and ambient air is permitted to enter the chamber so that the thermoplastic film molds more or less onto the product since there is a vacuum on the product side of the film and ambient air pressure on the other side of the film. Australian Patent No. 245,774 which issued to Colbros Proprietary Limited et al on Jul. 16, 1967 discloses a vacuum skin packaging process in which an article to be packaged is inserted within the lower half of a vacuum chamber on a backing board, a thermoplastic film is placed over the open face of the lower half of the chamber, the chamber is closed and both halves are brought to essentially the same state of vacuum, the film is heated and softened, and then atmospheric air is introduced into the upper half of the chamber so that it alone forces the thermoplastic film down around the product and against the backing board.
In another prior art version of vacuum skin packaging, disclosed in U.S. Pat. No. 3,491,504, which issued to W. E. Young et al on Jan. 27, 1970, heat softened film is physically moved down over a stationary product and, in connection with air pressure, the softened thermoplastic film is molded onto the product.
In U.S. Pat. No. RE.30,009, which was reissued on May 29, 1979 to Richard R. Perdue et al, a thermoformable or heat softenable film sheet is drawn by differential air pressure against the concave interior surface of the upper portion of a vacuum chamber, the film is then heated by surface contact, and then, after evacuation of the chamber, air pressure is used to blow the heat softened film down over the product and against the backing board. The resulting package comprises the product positioned on the backing board which is gas impervious and the product is held there by the thermoformable film which has been formed around the product in the exact shape of the product so that it appears to be a "skin." The thermoformable film, as stated previously, is also gas impervious and usually will consist of a number of layers each of which performs a specific function. The product contact and backing member contact layer will be a sealing or heat sealable layer, an interior layer will typically be a barrier layer which comprises a vinylidene chloride copolymer (PVDC) or a hydrolyzed ethylene/vinyl-acetate copolymer (EVOH), and the outer surface layer will be an abuse layer to protect the barrier layer from scratches, pin holes, or from moisture attack.
As set forth above, the mechanics of vacuum skin packaging require an impervious tray or support member. Typical pervious foam trays are coated with an impervious or barrier material for use in VSP.
Also as set forth above, peelable VSP packages are desirable and involve peeling a barrier layer or film or the like from the package to expose a non-barrier layer. The layers to be peeled, however, are sealed to the support member or tray which, it should be recalled, must be a barrier or impervious tray. Because the barrier and non-barrier layers or skins are sealed to the barrier film of the tray, peeling can destroy the packaging by peeling up the barrier film of the tray. This is particularly a problem because the bond between the tray and the barrier film is typically a relatively weak bond. Prior art FIGS. 2 and 3 illustrate the intended operation of such a package (FIG. 2), and the above-described undesirable peeling of the barrier film of the tray which may occur instead (FIG. 3).
It is accordingly a primary object of the invention to provide a package and a method for packaging a product wherein removal of a peelable layer does not damage or destroy the barrier film of a foam barrier tray.
It is another object of the invention to provide such a package having a manual pull tab for initiating peeling of the peelable barrier layer.
Other objects and advantages will appear hereinbelow.